The invention relates to an apparatus for measuring biological signals, which is capable of displaying marker lines on a time axis in synchronism with a particular position of a reference wave so that, if an electrocardiogram is selected as the reference wave, a plurality of other biological signals can be monitored in comparison with the electrocardiogram.
A polygraph, which is a multichannel monitoring apparatus, can monitor a plurality of biological signals such as an electrocardiogram, a pulse wave, a phonocardiogram, and blood pressure waves measured during a cardiac catheter examination while displaying them simultaneously on the screen of a monitor or can record the plurality of biological signals simultaneously by a printer.
When biological signals to be monitored are circulatory ones, a plurality of biological signals are generated simultaneously in synchronism with a cardiac cycle. It is for this reason that the waveforms of the biological signals displayed on the monitor screen or recorded on the recording sheet simultaneously are studied in phase with the cardiac cycle. In this case, a biological signal whose cardiac cycle is distinct is picked up as a reference for comparison among biological signals.
For example, in the case of a phonocardiogram that is an acoustic waveform generated as a result of the mechanical activity of a heart, it is difficult to distinguish only by the phonocardiogram a sound I generated as a result of a close of atrioventricular valves from a sound II generated as a result of a close of semilunar valves. Thus, the operation of distinguishing the sound I from the sound II with reference to an electrocardiogram is involved.
In the case of a blood pressure wave measured during a cardiac catheter examination, the waveform and amplitude thereof vary greatly depending on the position at which a catheter is inserted. As a result, it is difficult to locate the part of the heart from which the waveform is obtained only by the blood pressure wave. Thus, an electrocardiogram is referred to, again, in order to study the blood pressure wave.
Electrocardiograms and pulse waves are often used as reference waveforms for other biological signals since their cardiac cycles are easy to be distinguished. The electrocardiogram is a biological signal generated at the beginning of a cardiac cycle. The starting point corresponding to a P wave and the end points corresponding to a QRS wave and a T wave represent breaking points of the cardiac cycle. The pulse wave is a circulatory biological signal easily obtained, from which it is easy to recognize the cardiac cycle. The start point of the waveform and a DN (dicrotic notch) represent breaking points of the cardiac cycle.
When monitoring a plurality of biological signals with the cardiac cycle as a reference, it has been conventional to temporarily stop the sweeping of biological signal waveforms displayed on the monitor screen and manually move the cursor to a particular position of, e.g., an electrocardiogram.
In the case of studying a plurality of biological signals recorded on a recording sheet, two waveforms have been compared with each other either by using the graduation of the recording sheet or by drawing a line by drawing at a timing corresponding to a particular wave position in, e.g., an electrocardiogram.
Thus, in the case of monitoring simultaneously a plurality of biological signals displayed on a monitor screen such as a CRT, comparison of other biological signals with, e.g., an electrocardiogram as a reference is difficult since the waveform is swept, thus making monitoring of the waveform in phase with the cardiac cycle difficult in the conventional art. It is for this reason that the practice of manually moving the cursor to an arbitrary position while stopping the sweeping of the waveform as often as necessary has been performed.
Further, in the case of monitoring biological signals recorded on a recording sheet, the points in time at which the significant waveforms of the biological signals are generated are different from one another. Since a graduation provided on the recording sheet keeps regular intervals, the graduation makes their monitoring in phase with the cardiac cycle difficult. It is for this reason that the practice of drawing a line on the time axis, matching a reference point of the cardiac cycle using a ruler, has been required.
These operations are not only time-consuming, but also not practical in that such operations often must be performed on all heartbeats.